Cellular activity of microRNAs dysregulated in breast cancer

Breast cancer is one of the major health problems worldwide and it is the second cause of cancer-related in women. Patients often develop resistance to the current therapies. For this reason, the identification of new specific clinical molecular markers and pharmacologic targets in cancer research is an ongoing challenge. Over the last years, microRNAs (miRNAs) have become one of the main subjects of study in the area of cancer genomics. They negatively regulate gene expression post-transcriptional by inhibiting translation and causing degradation of target mRNA. More than a thousand miRNAs exist in the human genome and each one can potentially regulate hundreds of mRNAs. By regulating the expression of target genes, miRNAs can have a tumor suppressor or oncogenic role. Therefore, miRNAs can play an important role in all the phases of cancer, like as initiation, progression, growth, apoptosis, invasion and metastasis. In a previous study based on miRNA profiling, in different solid tumors, comprised breast cancer, and normal tissues, several miRNA were reported to be over- or down-regulated in solid tumors in comparison to normal tissues (Volinia et al. Genome Res. 2010). In other scientific reports other miRNAs were positively or negatively correlated with tumor progression (Volinia S. and Croce CM. PNAS 2013). Starting from these literature data, we decided to analyze the in vitro effect of the administration of this tumor-related miRNAs in order to verify their effect on the viability and transcriptional regulation in breast cancer cell line, in order to gain experimental evidences on their actual involvement in the tumor illness. Firstly, we have chosen 10 different cell lines of breast cancer origin (MCF-7, MDA-MB-231, MDA-MB-468, MDA-MB-361, SKBR3, T47D, BT474, ZR75.1, MDA-MB-453, HBL-100) and on 2 cell lines of breast normal epithelium (MCF10A and 184A1). Genomic analysis revealed presence of a complex panel of cancer-related mutations, and the cell lines were different in term of cell growth. We checked also the miRNA levels inside cell lines. Two groups of primary solid tumor-related (23 miRNAs: hsa-miR-126*, hsa-let-7d*, hsa-miR-326, hsa-miR-320c, hsa-miR-302a, hsa-miR-222, hsa-miR-218, hsa-miR-210, hsa-miR-206, hsa-miR-203, hsa-miR-202, hsa-miR-181a, hsa-miR-142, hsa-miR-145, hsa-miR-143, hsa-miR-138, hsa-miR-130b, hsa-miR-126, hsa-miR-99a, hsa-miR-28-5p, hsa-miR-33b, hsa-miR-26b, hsa-miR-21) or progression-related (15 miRNAs: hsa-miR-9, hsa-miR-10a, hsa-miR-25, hsa-miR-27, hsa-miR-30a, hsa-miR-93, hsa-miR-103, hsa-miR-148b, hsa-miR-151, hsa-miR-301a, hsa-miR-328, hsa-miR-484, hsa-miR-615, hsa-miR-874, hsa-miR-1307) miRNAs were transiently transfected into cells, and viability was assessed. We were able to experimentally identify two groups of miRNAs which were able to significantly increase or decrease cell viability. The miRNAs that showed to increase cellular viability in five out twelve cell lines were: miR-130b, miR-138, miR-210, miR-148b and miR-1307. On the other hand, miR-93, miR-126 and miR-145 displayed a significant inhibitory effect on cell viability in five out twelve cell lines. These miRNAs were further investigated for their capacity to affect cell migration, cell invasion, and genome profiling. The main outcome of our work has been the identification from a wide list of cancer-related miRNAs of few of them involved in the in vitro regulation of cell growth and invasion. As a first attempt to identify target genes commonly regulated in vivo and in vitro, we have bioinformatically identified, in a first not exhaustive screening, PTEN and DICER1 genes, which in vivo and in vitro negatively correlated with miR-210 and miR-130b, respectively.